The findings from this study should be considered in the context of a number of limitations. First, the sample was recruited primarily to study substance dependence traits. There is high comorbidity between PTSD and substance dependence, and although we have replicated findings from other groups relevant to PTSD in this sample (11,12,18,41), it is possible that the findings are not applicable to PTSD in other patient populations. In addition, the size of the GWAS and replication samples was small, and thus the statistical power was low. Finally, our replicated results are specific to EA populations. Previous work regarding FKBP5 (11,12) showed gene×environment effects were applicable only to AA populations. We may, therefore, conclude that the genetic underpinnings of PTSD are at least partially different in these two populations.
